RadButton has different render modes that can change the actual HTML markup that is rendered. They are exposed via the RenderMode property that can have four possible values - Classic, Lightweight, Mobile and Auto. This functionality was introduced in the Q1 2015 version.

The possible options are:

Classic—this mode is the rendering that has been used before. It remains without changes and it is the default value of the property. In this mode span elements and background images (in several sprites) are used to create the layout (including rounded corners, shadows, icons etc.).

Lightweight—this mode emphasizes on semantic HTML and CSS3. It reduces the amount of markup the control renders and makes it easier to customize. This also reduces the number of image sprites required by the control. All of this decreases the overall size and complexity of each skin, including custom ones.

Mobile—this mode is currently not supported. If you set it, the mode will fall back automatically to Lightweight.

Auto—this mode makes each control choose the appropriate rendering mode according to the used browser—Classic or Lightweight.

important

RadButton, as well as the other controls included in the Telerik® UI for ASP.NET AJAX suite that utilize render modes, support only one type of render mode per page. This includes mode being set for a standalone RadButton. All such controls must have the same RenderMode on a given page.This also includes instances from user controls and master pages.

RadButton, RadCheckBox, RadImageButton, RadLinkButton, RadPushButton and RadToggleButton share the same rendering and stylesheets, so all their instances on the same page must have RenderMode=Lightweight because this is the only mode supported by all of these controls.